Overview

Brief Summary

Biology

Water voles are herbivores, feeding on a huge variety of waterside vegetation (2), and consume 80 percent of their body weight each day (5). Their burrow systems have several horizontal layers to guard against flooding (5), and there is usually an underwater entrance to provide this strong swimmer with a safe route in and out (2). Above-water entrances to the burrow can often be identified by a 'lawn' of cropped grass around the hole (2). During the breeding season, the boundaries of female's ranges are marked with latrines, piles of flattened droppings where scent marking occurs. Each year between April and September, one to five litters consisting of three to seven blind, naked pups can be produced. Occasionally, dominant daughters may oust their mother from her territory after bouts of teeth chattering, tail beating and even boxing with the forefeet. In winter, a female, her daughters and unrelated males share a communal nest, but they do not hibernate (7).

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Description

The water vole is the largest and most famous of the British voles (5). 'Ratty' in Kenneth Grahame's Wind in the Willows was not a rat, but a water vole; water rat is a local name for the species (5). Water voles have a short hair-covered tail, a blunt, rounded nose, and a small chubby face with small ears. They have a rich chestnut-brown coat (2), but individuals in Scotland often have black fur. The fur traps air that provides thermal insulation when swimming, and they also possess flaps of skin in the ear that prevent water from entering (5).

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Distribution

Range Description

There is much confusion between Arvicola amphibius and A. scherman and the distribution of both taxa should be considered tentative. Arvicola amphibius, as understood here, has a large range extending from France and the United Kingdom in the west, through much of continental Europe and Russia, as far as the Lena Basin and Lake Baikal in Siberia (Russia). Its range extends north of the Arctic circle and south into Iran and the Near East (Shenbrot and Krasnov 2005).

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Range

The water vole is widely distributed throughout Europe from the UK to eastern Siberia (5). It is widespread throughout Britain but is generally restricted to lowland areas beside water (2). Once a very familiar mammal of the British countryside, the population has undergone one of the fastest and most serious recent declines of any British mammal (5). The species has been in decline for many decades (6), and a national survey in 1996 to 1998 showed that the water vole had been lost from a massive 94 percent of sites (5) and had vanished from entire catchments in northeast Scotland, North Yorkshire and Oxfordshire (5).

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Jefferies 1996-1998 study on water vole distribution in the UK shows a precipitous drop (88%) in water vole population since his previous study in 1989-90. He records that the estimated UK summer population of voles had declined from 7,294,000 to 875,000 in only eight years. He also records the loss of 69.62% of occupied sites in the same time period. Pressure from sheep grazing and feral mink predation were found to be the main reasons for this.

With a dense coat of fur, small, rounded ears, and short tail, A. amphibius resembles other voles of similar size. Water voles are relatively large voles. Their pelage is thick and extends from the head to the end of the tail. Coloration ranges from light to dark brown on top (sometimes black); and from white to slate gray on their underside. This coloration makes them difficult to see in the dense vegetation they prefer. Claws on each of the feet are well developed, and flank glands on the sides of the body used to mark territory are visible most of the time as well. Water voles possess the typical rodent dental formula and posses continuously growing cheek teeth (Niethammer, 1990; Nowak, 1991).

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Ecology

Habitat

Habitat and Ecology

This large vole is adaptable and survives in a range of habitats around rivers, streams and marshes in the lowlands and the mountains (Harrison and Bates 1991). It is a strong swimmer and climber (Harrison and Bates 1991). It occurs around streams and irrigation ditches. In Fennoscandia and locally in the Balkans, they live fossorial life during winter months. Steep riverbanks with lush grass and vegetation are preferred. May be active at any time, but are most active at dawn and dusk. Mainly vegetarian, feeding primarily on succulent vegetation, but also consumes some insects, mollusks, and small fish; roots, bulbs and tubers in the winter (Reichstein 1982, Harrison and Bates 1991). Reproduction occurs during the warmer months of the year and may begin as early as February in mild years. Gestation period is 21 days. Females produce 2-4 litters per year. Average litter size between 4-6 young.

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Water voles live in the banks of rivers, streams, ponds, and other bodies of water that maintain a fairly constant water level. They prefer areas with good vegetation cover. They are mainly found in lowland areas near waterways but also sometimes occur in gardens and fields. Water voles dig lengthy burrows, ranging from 34 m in the winter up to 74 m in the summer. Burrows contain one or two nests and in the winter contain storage chambers for food (Niethammer, 1989; Nowak, 1991).

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Trophic Strategy

The diet of Arvicola amphibius is comprised mainly of various forms of vegetation. This includes different types of grasses, herbs, and sometimes fruits and seeds. Water voles also feed on the roots of some plants, causing extensive root damage and sometimes destruction of crops. In addition to vegetation, water voles will sometimes supplement their diet with water snails, freshwater mussels, and mollusks (Cobet, 1966; Thompson, 1964).

In the winter, water voles usually maintain at least one chamber in the burrow as a place to store grasses and other food to feed on during lean winter months. They do not live entirely off this store, and will still forage for food during the winter (Nowak, 1991).

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Associations

Water voles are an important prey base for many small to medium-sized predators. They are also important in nutrient cycling through their burrowing and grazing activities in the ecosystems in which they live.

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Water voles seek safety in their burrows and restrict their movements mainly to areas of dense vegetative cover to avoid predation. Their prodigious reproductive rates generally help to maintain viable populations under predation stress by natural predators. However, non-native American mink (Neovison vison) are decimating water vole populations in the British Isles.

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Lifespan, longevity, and ageing

Maximum longevity: 2.5 years (captivity) Observations: These animals live on average less than 6 months in the wild. It has been reported that they live up to 5 years in captivity (Ronald Nowak 1999), which is doubtful even if not impossible. Record longevity in captivity is 2.5 years (Richard Weigl 2005).

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Reproduction

Male home ranges overlap those of several females and males continually compete for access to receptive females. Research using microsatellite analysis of genetic patterns confirmed that the mating system was promiscuous (Stewart et. al., 1999).

Arvicola amphibius undergoes one mating season per year, usually ranging from early spring (April/March) to late summer/early autumn (August/October). During this time water voles can have up to four litters with an average number of four to six young each. The gestation period is short, 21 days, and postpartum estrus and mating usually occurs shortly after birth. Newborn weight is usually 5g, with young opening eyes around 5 days, and becoming weaned 14 to 21 days after birth. Sexual maturity is reached during their first summer, if born early in the season, or in the following mating season (Bazhan et al., 1996; Nowak, 1991). Females may mature as early as 5 weeks of age.

Breeding interval: Water voles can have up to 4 litters in each breeding season.

This species has a wide distribution, and is considered a pest in parts of its range. The population size has not been quantified, but it is not believed to approach the thresholds for the population size criterion of the IUCN Red List (i.e. less than 10,000 mature individuals in conjunction with appropriate decline rates and subpopulation qualifiers). Although there are ongoing declines in some range states (such as Britain, Italy, and the Netherlands), the overall population trend is believed to be stable at the global level. For these reasons, it is evaluated as Least Concern.

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Some humans have attempted to take actions against water voles in efforts to minimize damage to crops (Neithammer, 1990). However, water voles are on the decline in some regions. For example, in England changes due to habitat and introduction of American mink, Neovison vison, is thought to be playing a large role in the decline of water vole populations (Storey, 2001). Conservation efforts are underway in various parts of the British Isles to protect water vole populations.

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Trends

Population

Population declines are evident in some European countries (e.g., United Kingdom, the Netherlands and Italy) (Saucy 1999, Battersby 2005). However, in many areas it is common and stable (in northern continental Europe it is considered a pest species). Even in optimal habitat, aquatic forms seldom occur at densities greater than 100 individuals per hectare (roughly equivalent to 15 individuals per 100 m of river bank)(Saucy 1999). In Fennoscandia and the Baltic area the aquatic form also shows population cycles in synchrony with other vole species. At high population densities, large scale damages on rice fields have been reported in Macedonia (B. Krytufek pers. comm. 2007). The water vole is thought to have been a common species in the Hula swamps of Israel until the area was drained in 1957 (Qumsiyeh 1996). In Azerbaijan, considered to be common in semi deserts, lowland and riparian forests, mountain forests and mountain grasslands and numerous in foothill and mountain steppes. The species is locally abundant in lush banks.

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Threats

Declines in aquatic populations in parts of western Europe have been attributed to habitat loss, water pollution, predation by introduced American mink Neovison vison and competition by the introduced muskrat Ondatra zibethicus. Population fragmentation is more pronounced in Mediterranean populations due to increased aridity. In Israel it was a common species in the Hula swamps until the area was drained in 1957; a very limited area of the original swamp habitat remains (Qumsiyeh 1996). In Anatolia and Iran, pressure on aquatic habitat for water resources and localized competition with Rattus norvegicus (i.e., Georgia). Local population extinctions and reductions have occurred in Turkey, Georgia and other parts of this range due to drainage of swamp habitat (Qumsiyeh 1996). It is considered an agricultural pest and extensive control measures in rice fields were carried out in Macedonia in the 1980s.

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The shocking decline in both range and numbers of the water vole is due to a number of factors. The large-scale loss and fragmentation of sensitive waterside habitats due to riverbank modification, drainage and flood defence works has been an important factor (5), as has the pollution of waterways and poisoning by rodenticides (3). Perhaps the most serious threat facing the beleaguered water vole is predation by the introduced American mink (3). When threatened, water voles often dive under water and kick up a cloud of mud to hide from predators. This does not fool the American mink, however, which is able to successfully hunt the water vole on land, in the water and even inside the burrow system. There is a correlation between the loss of water vole sites and American mink presence (5), and the introduced mink has even resulted in local water vole extinctions (2).

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Conservation

It is likely that the water vole will become extremely rare in areas colonised by American mink; the elimination of American mink is unrealistic, but numbers can be controlled in key areas in an attempt to ease the pressure on the water vole. Habitat enhancement such as the encouragement of a broad variety of waterside vegetation and recreation of natural features such as water meadows and oxbow lakes could benefit the species. Under the Wildlife and Countryside Act 1981, it is an offence to disturb, obstruct or damage water vole burrows. A booklet has been produced by English Nature, providing guidance on the water vole for planners and developers (8). Research into the ecology and habitat needs of this species is essential, as little work has been carried out on it due to its previously common status (3).

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Relevance to Humans and Ecosystems

Benefits

Negative economic impacts from A. amphibius on humans stems mainly from the destruction of human crops such as beans, peas, and some forms of apple trees (Niethammer, 1990). In rare circumstances they have also been known to weaken river banks due to their extensive burrowing (Thompson, 1964)

In addition to crop damage and bank damage, A. amphibius is also known to sometimes carry and transmit tularemia. The disease affects mostly wild rodents and rabbits, but can be transmitted to humans by contact with animal flesh or tick bites (Nowak, 1991; WebMD, 1999).

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Wikipedia

European water vole

The European water vole or northern water vole, Arvicola amphibius (formerly A. terrestris), is a semi-aquaticrodent. It is often informally called the water rat, although it only superficially resembles a true rat.[3] Water voles have rounder noses than rats, deep brown fur, chubby faces and short fuzzy ears; unlike rats their tails, paws and ears are covered with hair.

In the wild, on average, water voles only live about five months. Maximum longevity in captivity is 2 and a half years.[4]

Contents

Water voles reach 140–220 millimetres (5.5–8.7 in) in length plus a tail of 55–70 millimetres (2.2–2.8 in) of this. Adults weights reported are variable. It is possible for large, optimal adults to weigh as much as 225 to 386 g (7.9 to 13.6 oz)[5] However, these are peak weights. Elsewhere the mean body mass has been reported as 60 to 140 g (2.1 to 4.9 oz), although this figure includes immature water voles.[6] The minimum weight to successfully breed as well as to survive winter is reportedly 112 g (4.0 oz) in females and 115 g (4.1 oz) in males.[7] As a species the mean body mass is claimed as 140 g (4.9 oz).[8]

Overall, European water voles are a uniform dark brown colour, with slightly paler coloration on the underside. Their pelage is quite thick and they are furred over their entire body, including their tail, unlike rats. Their dark colour allows them to blend in well in the densely vegetated areas they inhabit.[9]

The binomial applied to the water vole is Arvicola amphibius, it was formerly known by the junior synonymA. terrestris. The confusion stems from the fact that Linnaeus described two species of water vole on the same page of the same work. Those two forms are now universally considered the same species. It has been recognized as A. amphibius (Linnaeus, 1758) because the first source to unite the two forms that Linnaeus had treated separately into a single species chose A. amphibius as the valid name.[1] The species is widely known by the synonym A. terrestris which for many decades was treated as the valid name.

Some authorities consider the southwestern water vole (Arvicola sapidus) to be the same species, but this is now generally considered to be distinct.[2][10]

In Britain, water voles live in burrows excavated within the banks of rivers, ditches, ponds, and streams. Burrows are normally located adjacent to slow moving, calm water which they seem to prefer. They also live in reed beds where they will weave ball shaped nests above ground if no suitable banks exist in which to burrow.

Water voles prefer lush riparian vegetation which provides important cover to conceal animals when they are above ground adjacent to the water body. Areas of heavily grazed and trampled riparian habitats are generally avoided.[11] Water voles may be displaced by the introduction of riparian woodland and scrub as they prefer more open wetland habitats away from tree cover.

As well as frequenting typical lowland wetland habitats dominated by rank marginal aquatic vegetation, water voles are also just as at home in areas upland 'peatland' vegetation where they utilise suitable small ditches, rivers and lochs surrounded by moorland up to 1000 m asl (e.g. northern Scotland).[12]

In Europe and Russia, they may venture into woods, fields, and gardens. They live under the snow during the winter.

Water voles mainly eat grass and plants near the water. At times, they will also consume fruits, bulbs, twigs, buds, and roots. In Europe, when there is enough food to last water voles a long time, water vole "plagues" can take place. Water voles eat ravenously, destroying entire fields of grass and leaving the fields full of burrows, during these plagues. Ecologists have discovered that normally vegetarian water voles living in Wiltshire, England have started eating frogs' legs and discarding the bodies. This has also been observed at a pond in Lincolnshire. The predation in 2014 was severe and no tadpoles were observed in the pond for the first time in about 8 years.It has been speculated that this is to make up for a protein deficiency in the voles' diet.[13]

Food remains alone are not a reliable indicator of the presence of this species, as other smaller voles can also leave remains of large grasses and rushes.[14]

The mating period lasts from March into late autumn. The female vole's pregnancy lasts for approximately 21 days. Up to 8 baby voles can be born, each weighing around 10 grams (0.4 oz). The young voles open their eyes three days after their birth. They are half the size of a full grown water vole by the time they are weaned.

Water voles are expert swimmers and divers. They do not usually live in large groups. Adult water voles each have their own territories, which they mark with fecal latrines located either near the nest, burrow and favoured water's edge platforms where voles leave or enter the water.[12] Latrines are known to be a good survey indicator of this species, and can be used to gauge abundance of animals.[15] They also scent-mark by using a secretion from their bodies (a flank gland), although this is not normally detectable during a field survey. They may attack if their territory is invaded by another water vole.

The water vole population in the UK has fallen from its estimated pre-1960 level of around 8 million to 2.3 million in 1990 and to 354,000 (other source: 750,000) in 1998. This represents a 90–95% loss. It is still declining dramatically: the most recent estimate for 2004 is around 220,000. This decline is partly attributed to the American Mink, an aggressive predator of the vole, together with unsympathetic farming and watercourse management which destroyed parts of the water vole's habitat.

On 26 February 2008, the UK Government announced full legal protection for water voles would be introduced from 6 April 2008.[18] This makes it an offence to disturb, damage or obstruct their breeding places.

The water vole is the UK's fastest declining mammal and efforts are under way to protect it and its habitat from further destruction. One aspect of water vole conservation in the UK is focused on non-linear habitats such as reed bed which support extensive networks or metapopulations. Other areas supporting healthy populations of water voles are large conurbations such as Birmingham and London and some upland areas where American Mink are scarce. Across the UK the Wildlife Trusts and other organisations are undertaking many practical projects to conserve and restore water vole populations.

Water voles have recently returned to Lindow Common nature reserve in Cheshire, UK, after many years of absence.[19] The reserve rangers credit this to conservation management, which included thinning of woodland.

Wetlands West (formerly the Severn and Avon Vales Wetlands Partnership) reports on work done as part of the Water Vole Recovery Project in the Berkeley Vale.[20] In Gloucestershire a new nature reserve for water voles was created in 2009/2010 at Nind (a former Trout Farm).

There are also indications that the water vole is increasing in numbers in UK areas where the European otter has made a return.[21]

A water vole named Ratty is a leading character in the 1908 children's book Wind in the Willows by Kenneth Grahame: the locality used in the book is believed to be Moor Copse in Berkshire, England, and the character's name "Ratty" has become widely associated with the species and their riverbank habitat, as well as the misconception that they are a species of rat.[22][23]

In the comic novel and film Cold Comfort Farm by Stella Gibbons, one of the characters, Urk, refers to the subject of his unrequited love, Elfine Starkadder, as his little water vole. Throughout the story, Urk spends a lot of time talking to the water voles on the farm.

C. S. Calverley a 19th Century writer of (among other things) light verse, in his poem "Shelter," beginning:

By the wide lake's margin I mark'd her lie--

The wide, weird lake where the alders sigh--

Tells of an apparently shy, easily frightened young female by a lakeside, who in the last line of the poem, it's revealed that:

^Ryland, K. and Kemp, B (2009). "Using field signs to identify water voles - are we getting it wrong?", In Practice, Bulletin of the Institute of Ecology and Environmental Management. 63, March 2009 (pp. 23-25).